I've read in the manual that after the Winter season one should clean the underside of the car (and engine compartment) to help prevent corrosion (expedited by salting, etc., although the gritters haven't been out so much my way). What's the best way to go about doing this: take it through a car wash with upward sprays; get out a bucket and brush and scrub, being careful around the tender bits (the so-called "equestrian" method ); or the garden hose with a shower attachment?